Pneumatic conveyors and the like for powdered and granular materials



Oct. 25, 1960 R. w. ALLEN EI'AL 2,957,727

PNEUMATIC CONVEYORS AND THE LIKE FOR POWDERED AND GRANULAR MATERIALS Filed Nov. 1'7, 1958 3 Sheetw-Sheei: l

Oct. 25, 1960 R. w; ALLEN ETAL 2, 57, 7

PNEUMATIC CONVEYORS AND THE LIKE FOR PQWDERED AND GRANULAR MATERIALS Filed Nov. 17, 1958 3 Sheets-Sheet 2 2,957,727 HE LIKE FOR ERIALS 3 Sheets-Sheet 3 Oct. 25, 1960 R. w. ALLEN ETAI.

PNEUMATIC CONVEYORS AND T POWDERED AND GRANULAR MAT Filed NOV. 17, 1958 United States Patent In the specification o f'our Patent No. 2,868,590, issued to the assignee of the present application, relating to pneumatic conveyors and the like for powdered and granular materials, means are described wherein in each of the several air ducts from a common source of air pressure, there is mounted upstream of the positions where the air mixes with the material to be conveyed (or upstream of positions where the air passes into diifusing elements), an air nozzle co-axial with and forming part of the associated duct, which nozzle at its inlet or upstream side converges rapidly to the nozzle throat, which has a cross-sectional area so related to the desired mass flow rate through the nozzle, that in operation the air velocity through the throat is approximately equal to the velocity of sound in the air at the temperature and pressure existing at the throat, the nozzle diverging from its throat at a small angle (e.g. not more than 12), the cross-sectional area at the delivery or downstream end of the nozzle being equal or substantially equal to that of the air duct, whereby a substantially constant mass flow rate through the several nozzles is obtained notwithstanding variations in the resistances of the systems downstream of the several nozzles. Means are also described whereby the mass flow rate in an air duct according to the invention can, subject to certain limitations, be adjusted by altering the absolute pressure of the air up stream of the nozzle by the use of a variable pressure regulating means provided at a position immediately upstream of the nozzle.

The object of the present invention is to provide simple and eifective means whereby the cross-sectional area of a nozzle according to our above mentioned specification can be adjusted to suit required conditions.

According to the present invention, a nozzle of the type described in our aforesaid specification comprises a tube co-axial with and forming part of an associated duct, which tube carries a nozzle element to give a nozzle throat, and a needle which extends substantially coaxially through the nozzle throat for reducing the effective cross-sectional area thereof.

With arrangements in accordance with the invention, one common size of nozzle element can be provided to suit the cross-sectional area of the air ducts employed in an installation and its throat area adjusted either by a relative movement between the nozzle element and a tapered needle or by selecting and inserting a suitably sized cylindrical needle so that the nozzle will suit any of a wide range of mass flow rate requirements.

Referring to the accompanying drawing:

Figure 1 is a longitudinal section through a nozzle in accordance with the invention, having an axially adjustable needle, an alternative needle also being shown.

Figure '2 is a longitudinal section through another nozzle in accordance with the invention, in which the nozzle element is axially adjustable.

Figure 3 is a cross section taken at I II-I H of Figure 2.

Figure 4 is a diagrammatic view of a pneumatic conpart 1 2 ,wl 1:ich engages a screwed nut member 13. The

Taylor-i y 2,957,727 Patented on. 25, 19 0,

2. veying system for powdered or granular material incor-. porating the present invention. I The nozzle shown in Figure 1 comprises a body having two parts 1 and 2 joined together at respective flanges 3 Iand Part; 1 aecommodates a nozzle element 5 having a steady taperconverging towards the part 2. Part 2 comprises an air feed tube, 6 and an extension 7 supporting a tapered needle 8, eo,-axially with the nozzle ele-, ment 5 The shank Of he needle 8 has a plain part 9, s pgorted in a bush 10' with-"sealing ring 11, and a threaded needle 8. is adjusted in; relation to the nozzle element- 5by rotating it '(the needle) from its back end 14 by means of a knob. or the like (not shown). To prevent unwanted: rotation of the needle 8' a lock-screw clamp 15 isfprovided. A: stop-collar 1 6 limits the inward adjustand a removable cover 17' prevents'easy tamperwith the adjustment, second needle 18 is provided and between the'two the whole'operation range otthe nozzle is covered. i

Alternatively, a cylindrical needle 40 may be used where continuous adjustment is not required. Step-bystep adjustment may be obtai ned'by the use of different sized needles. i i i If a continuous range of adjustment is not required, adjustment in steps may be provided by diiferent sized cylindrical rods. In this case the thr'eading arrangement for advancing the needle may be dispersed with and replaced by means enabling the diiferent rods, as required, to be clamped with the rod extending co-axially through the nozzle element? j i In the embodiment of the invention shown in Figures 2 and 3 a slidably mounted nozzle element 20 has on part of its exterior surface a screw-thread 21 which'engages an internally screwed locating ring 22 rotatably mounted in a recess formed between flanges 23 and 24 of nozzle tube parts 25 and 26 respectively. The ring 22 is provided with manually operable rotating means in the form of a captive spring-loaded tommy bar 27 arranged to engage holes 28 in the ring 22 when suitably depressed. Throughthe medium of the engaging screw-threads, rotation of the locating ring 22, in quarter turns, causes the nozzle element 20 to slide axially relative to a fixed tapered needle 29, held by a three-legged spider 30, thereby changing the cross-sectional area of the nozzle throat. The slidable nozzle element 20 is prevented from rotating by a key 31 which locates in a slot 32 in the tube 25, the said key providing a simple means whereby the relative position of the nozzle element 20 can be checked against a fixed scale 38. A further angular scale may also be provided in association with the tommy bar.

Figure 4 shows a pneumatic conveying system similar to that described in U.S. Patent No. 2,868,590, issued to the assignee of the present application. The system comprises two main compressed air supply pipes 50 and 51 which lead from a common pipe 52, the two pipes 50 and 51 leading to branches 53, 54 and 55, and 56, 57 and 58 respectively, in each of which is located a nozzle 59 of a construction as shown in detail in Figure 1. From the nozzle 59 in the branches 53, 54 and 55 the compressed air leads to and passes through a rotary valve 60 which receives the grain or powder to be conveyed the grain or powder is separated from the air and delivered through a valve 66 to a discharge pipe 67 whilst the separated air is delivered by the branch 68.

The nozzles 59 in the branches 56, 57 and 58 deliver compressed air to spaces 69 between a porous base 70 over which the material flows from the hopper 61 to the rotary valve 60. Such air delivered through the porous. base fluidises the material so that it flows freely from the base of the hopper and does not become blocked or clogged up.

There are pressure regulating valves 71 in the branches 53, 54 and 55 in advance of the nozzles 59 and pressure gauges 72 and 73 are associated with each nozzle in said branches, the gauge 72 indicating the pressure difierence across its nozzle and the gauge 73 indicating the pressure immediately upstream or in advance of the nozzle relative to atmospheric pressure.

. With the arrangement shown, and nozzles 59 and the regulating valves 71 adjusted having regard to the readings of the gauges 72 and 73 to ensure correct conveying at maximum capacity, any reduction of pressure in the air duct into which a nozzle delivers its air, such as Would occur for example with a reduction of the rate of flow of material into the air stream from the valves 60, whilst causing a change in the indication given by a gauge 72, would not cause any change in the indication given by a gauge 73. It will be appreciated that the optimum setting .of each valve 7-1 is the one which provides the lowest pressure in advance of its associated nozzle 59 which will remain constant for all conditions of conveying up to maximum capacity.

The nozzles 59 in the branches 56, 57 and 58 ensure that for a given air pressure at the inlet side of the nozzle, there will be a constant mass flow rate through the nozzle notwithstanding considerable variations in the pressure at the delivery side of the nozzle due to variations in the resistance of the material on the porous base to the flow of the fiuidising air therethrough.

What is claimed is:

l. A pneumatic conveying system comprising a plurality of air ducts operating in parallel for conveying a plurality of air streams, each said airstream mixing with powdered and granular material to be conveyed, a single source of conveying air for said air streams, a nozzle in each air duct upstream of the mixing of the air streams with said powdered and granular material to be con- Veyed, each said nozzle comprising a tube co-axial with and forming part of the associate duct, each said tube carrying a nozzle which at its upstream end converges rapidly to the nozzle throat, and which diverges from its throat at a small angle, the cross-sectional area at the downstream end of the nozzle being substantially equal to that of the air duct, and a needle which extends substantially co-axially through the nozzle throat and is arranged relative to the throat of the nozzle element to provide that unique cross-sectional throat area which ensures that for a desired mass flow rate through the nozzle the velocity of the air passing through the throat will in operation be equal to the velocity of sound in the air at the temperature and pressure existing at the throat.

2. A system as claimed in claim 1 wherein the needle of the nozzle is tapered and means are provided for elfecting relative axial movement between the nozzle element and the needle for varying the effective throat area.

3. A system as claimed in claim 1 wherein the needle of the nozzle is cylindrical and means are provided for readily interchanging it with other needles of different cross-sectional areas.

4. A system as claimed in claim 2 wherein the nozzle element is held fixed in the said tube and the tapered needle has a cylindrical threaded portion enabling the axial position of the needle to be adjusted by rotation of the needle relative to the said tube.

5. A system as claimed in claim 2 wherein the tapered needle is mounted within the said tube by a spider and the nozzle element is slidable within the tube for axial movement relative to the needle.

6. A system as claimed in claim 5 wherein the nozzle element has on part of its exterior surface a screwthread which engages an internally threaded locating ring rotatably mounted in a recess in said tube, said ring being provided with manually operable rotating means in the form of a captive tommy bar adapted to engage holes in the locating ring when suitably depressed, and means being provided to prevent rotation of the nozzle element.

References Cited in the file of this patent UNITED STATES PATENTS 854,641 Haley May 21, 1907 1,766,554 Sieber June 24, 1930 2,061,852 Schweitzer Nov. 24, 1936 2,403,751 Palmer July 9, 1946 

